A flaw in Microsoft's Internet Information Server (IIS) versions 4 and 5 -- software used to run an estimated 6 million Web servers worldwide -- can let an attacker execute code of his choice on the server, the company said Friday. The security hole is the second found in IIS this week and at least the fourth identified since the beginning of May.
This hole results from a vulnerability in a component of the Front Page Server Extensions (FPSE) which ship with IIS; Front Page is Microsoft's visual Web page builder and uses special server extensions to provide additional functionality. The component, the Visual Studio RAD (Remote Application Deployment), is an optional tool not installed by default with either FPSE or IIS and is used to help developers create software faster and easier.
The bug in the component would allow an attacker using a specially-designed packet to overflow the tool's memory buffer and run code of his choice. Normally that code would only be run in a mode that would restrict the damage it could do, but certain circumstances can let the code run in a more powerful context that make the system more vulnerable, the company said.
Microsoft does warn users that the Visual Studio RAD component should not be installed on Web servers in public use and warns users at the time of installing the component that it should be used only for internal development. The user must click past the warning in order to install the component, the company said.
Front Page Server Extensions are included in Office 2000, Office XP, Windows Server 2000, Windows Advanced Server 2000 and can be installed on Windows NT 4. The bug was discovered by Chinese security firm NSFocus Information Technology Co. Ltd.
Earlier in the week, Microsoft said that a flaw in IIS could allow an attacker to take full control of an affected Web server. Two other flaws found since May allowed server compromises or Denial of Service attacks.